A Kremlin official voiced concern over the reported U.S. plans when he spoke to reporters on Wednesday.

"Certainly, it's another, unfortunately, very serious step," Russian presidential press secretary Dmitry Peskov said. "Unfortunately, if this step is implemented -- and we can say they are confidently advancing towards its implementation, it may disrupt the strategic balance in Europe and therefore will clearly make Russia take corresponding countermeasures to re-establish the balance."

Peskov was not specific as to what exactly these countermeasures would include.